Hydrogen migration in hypoelectronic biicosahedral metallaborane structures

Abstract

The biicosahedral metallaboranes CpMB₂₀H₁₇ (M = Pd, Pt; Ru, Os; Mo, W) and CpM′CB₁₉H₁₇ (M′ = Rh, Ir; Re; Ta) have been investigated by density functional theory to supplement the earlier work on the first-row transition metal derivatives CpMB₂₀H₁₇ (M = Ni, Fe) and CpCoCB₁₉H₁₇. The CpMB₂₀H₁₇ (M = Ni, Pd, Pt) and CpMCB₁₉H₁₇ (M = Co, Rh, Ir) systems have the ideal 46 skeletal electrons by the Jemmis rules. Their lowest energy structures have the metal atom in the meta position of the biicosahedron. Hydrogen migration occurs in the low-energy structures of the hypoelectronic systems CpMB₂₀H₁₇ (M = Fe, Ru, Os; Mo, W) to give one or two M–B biicosahedral edges bridged by hydrogen atoms. In CpReCB₁₉H₁₇ and one of the CpTaCB₁₉H₁₇ structures more extensive hydrogen migration occurs to give low-energy structures having terminal M–H bonds and metal vertices of a degree of at least 6. The CpTaCB₁₉H₁₇ system also has a low-energy structure in which the TaCB₁₉ biicosahedron becomes distorted enough to provide a degree 8 vertex for the tantalum atom.